I have a SQS queue and a Lambda which reads messages from the queue. I have a Dead Letter Queue (DLQ) configured and working. I can see failed messages being delivered to the DLQ, its "Messages Available" in the AWS Console goes up.
When AWS moves the messages to the DLQ will this be logged in Cloud Watch?
By "logged", I mean an entry/row/event created in CloudWatch that:
indicates that a message has been delivered to a DLQ
ideally specifies:
DLQ name
some message/event unique id
lambda that was processing the message
optionally specifies the message body/payload
Related
I'm reading aws documents on deadletter queue and re-drive policy, and the document mentioned "The redrive policy specifies the source queue, the dead-letter queue, and the conditions under which Amazon SQS moves messages from the former to the latter if the consumer of the source queue fails to process a message a specified number of times".
However, even the document mentioned "message process failed" several times, I do not understand how sqs detects a message processing failure (and thus triggers re-drive or move to the dead letter queue.)
From what I understand, consumer applications call receiveMessage to retrieve the message from SQS, then process the message. The processing function is not passed in to receiveMessage as a lambda. So how does SQS know that message processing has failed?
When a client (e.g. a lambda function) gets a message from the queue, it has limited time to call DeleteMessage. Each msg has also visibility timeout. If the msg is not deleted by the client within the visibility timeout, SQS "assumes" that the processing failed.
Such messages can be then forwarded to SQS depending on how many failed attempts you setup to tollerate.
Trying to write some tests for my AWS SQS Queue and its associated Dead letter queue. I want to somehow in my tests force the message from the queue to its DLQ, then read from the dlq to see if the message is there.
Reading from the DLQ is no problem. But does anyone know a quick and easy way I can programmatically force an sqs queue to send a message to its associated DLQ?
The Dead Letter Queue is simply a SQS Queue, so you could send a message to it like you would any other queue.
The DLQ is configured when you create your normal queue and you need to pass a arn of a queue that will be used as DLQ.
When you configure your DLQ you set the maxReceiveCount (Maximum receives on the console) that is the number of times a message is delivered to the source queue before being moved to the dead-letter queue. When the ReceiveCount for a message exceeds the maxReceiveCount for a queue, Amazon SQS moves the message to the dead-letter-queue.
If want to test the process to send messages to DLQs, you need to force in your tests an error on the queue messages' processing to send a message to the DLQ queue, this will be the best way to understand if the errors are going to the queue correctly.
The process to send messages to the DLQ can be done in the following ways:
You explicitly send a message to the DLQ, if you found some error and do not want to process the message or delete at that time.
If you read the messages more times than the maxReceiveCount and do not process the message (read and delete from the queue) the AWS SQS service will understand that you are having problems on that message and will send automatically to the DLQ for you. (eg. maxReceiveCount equals 1 and your read the message and did not delete 2 times)
To understand more about DLQs, take a look here: Amazon SQS dead-letter queues.
I'm wondering what would happen if there was an SNS topic having messages written to it, but for a period of time, there is no SQS queue. Let's say there was a container which normally was subscribed to the SNS topic to handle such messages, but it crashed and burned and spent 10 minutes getting resurrected; what would happen to any messages written to that topic, during which there is no queue? Do they disappear forever, or do they wait politely until some queue comes along, subscribes and picks up said messages?
They disappear forever.
SNS cannot know that some subscriber wants to subscribe but simply cannot right now. The topic either has subscribers or it does not. All current subscriber get the message, all future ones do not.
If you have subscriber but the delivery fails there is some SNS specific behaviour in regards to retries: https://docs.aws.amazon.com/sns/latest/dg/sns-message-delivery-retries.html
If the subscriber fails to get the message, a retry mechanism in SNS kicks in as explained in the AWS docs:
When the delivery policy is exhausted, Amazon SNS stops retrying the delivery and discards the message—unless a dead-letter queue is attached to the subscription.
For SQS subscriber retry can be up to 100,015 times, over 23 days
If SQS Queue goes down then message won't disappear , Let's discuss this scenario:
Retry Policy :-** Let's say you set "Number of retries" as n and "Retry-backoff function" as Linear(you can select any other retry-backoff function) in SNS topic , then if SQS is not available then SNS will retry to send that message to subscriber(SQS) n number of times based on the "Retry-backoff function" .
But if you set Number of retries as 0 then your message will delete from SNS topic immediately if Subscriber(SQS) is not available
I'm trying to send s3event message to rabbitmq by invoking AWS lambda function. I have configured SQS as my dead letter queue(DLQ).
I know the message is sent to DLQ when there failure in invocation of lambda or situations like timeouts or resource constraints.
My question is ,I want to send event message to DLQ from inside lambda function on certain condition like if rabbitmq is down or some other condition of my interest.
Is there any possiblity for the same? Should I throw exception or there is some other better approach to send event message to DLQ.
I'm using java for development and connecting to rabbitmq from my lambda function.
The DLQ is simply an SQS Queue, so you could send a message to it like you would any other queue. You would want it to be formatted the same way that Lambda natively puts message in the DLQ so that whatever processing you have on the DLQ can perform the same way for all messages. You would want to ensure that you treat the lambda as successfully executed in this instance though so that the normal DLQ process doesn't pick up the same message twice.
In the DLQ setting of a Lambda you specify a SNS topic or a SQS Queue. In your setup you have configured the DLQ to be a SQS queue. This is a regular SQS Queue. Using the SQS Java SDK you can post a message to that SQS Queue.
here are few references:
https://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/sqs-send-message.html
To get the Queue URL you can use these:
https://docs.aws.amazon.com/AWSSimpleQueueService/latest/APIReference/API_GetQueueUrl.html
Or through Java:
https://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc/com/amazonaws/services/sqs/AmazonSQSClient.html#getQueueUrl-java.lang.String-
We can send/receive messages to/from AWS SQS Queue, But Can we update message content which is already in SQS Queue ? If possible , How ?
Once a message has been sent to an SQS queue (standard or FIFO), the message is immutable. Additionally, it isn't possible to ask SQS for a specific message by its ID.
The message is essentially inaccessible until received by a consumer.
(Viewing messages in the AWS console might seem to be an exception, but it isn't -- the console acts as a consumer, receives messages, and then resets their visibility timeout so they return to the queue for subsequent redelivery.)